The present invention relates to a substrate transfer apparatus, and more particularly to a substrate transfer apparatus which can accurately transfer a substrate such as a semiconductor wafer for a long term while suppressing an influence of heat from a film growth apparatus or the like, to a level as low as possible.
In a semiconductor production step, a film growing process such as CVD (Chemical Vapor Deposition) or sputtering is performed in order to form an integrated circuit on a semiconductor wafer (hereinafter, referred to as "wafer") made of silicon or the like. In such a film growing process, a given processing gas and the like are supplied into a vacuum vessel which is evacuated and heated to a given high temperature, a wafer is transferred into the vessel by a transfer apparatus, and a film of a predetermined material such as a metal is then grown on the wafer. After the film growing process, the wafer is carried out by the transfer apparatus to be transferred to the subsequent step or the like.
In such a wafer transfer apparatus, as shown in FIG. 14, a first arm 2, a second arm 3, and a third arm 4 are rotatably coupled in sequence to an upper portion of a driving mechanism 1. An end effector 5 on which a wafer is to be placed is disposed at the tip end of the third arm 4. In order to reduce the contact area with a wafer, the tip end of the end effector 5 is fork-shaped, and the end effector is made of ceramics for the sake of prevention of contamination, insulation, and the like. When the first to third arms 2 to 4 are elevated in the direction Z by driving of the driving mechanism 1, the end effector 5 is elevated in the direction Z, and, when the first to third arms 2 to 4 are rotated, the end effector 5 is rotated in the direction .theta. and moved in the R-axis.
As shown in FIG. 15, the end effector 5 has a fork-like portion 6 on which a wafer W is to be placed, and is made of ceramics as described above. The basal portion of the end effector 5 is fittingly fixed to a fitting portion 7 which is formed in the tip end of the third arm 4. The third arm 4 is made of aluminum for the sake of prevention of contamination and the like.
In such a film growth apparatus for CVD, the wafer W is always exposed to a high temperature during a film growing process. This high temperature is transmitted from the wafer W to the third arm 4 made of aluminum which is excellent in thermal conductivity, via the end effector 5 on which the wafer W is placed, and further transmitted from the third arm 4 to the second arm 3, the first arm 2, and the driving mechanism 1. As a result, the transfer apparatus is affected by heat from the film growth apparatus.
When a transfer apparatus is affected by heat from a film growth apparatus as described above, a magnetic fluid used in the transfer apparatus may be changed in quality and the sealing performance of a magnetic fluid seal may be impaired. Furthermore, grease or a belt in the transfer apparatus may be changed in quality or deformed, so that the life period of the grease or the belt is shortened. Moreover, heat of a relatively high temperature may be transmitted to a metal part of the transfer apparatus, and the metal part is thermally expanded, so that the accuracy of the part is lowered.